Case study: Hospital patient tower
During the design of a 135,600-square-foot patient tower, the focus by the design team was a combination of patient comfort and system reliability. The IMEG engineering team met with facilities and discussed the ramifications of system failures and the risk those failures imposed on patients, staff and the public.
More than 70 new patient rooms were planned and the rooms feature dedicated patient, staff and family areas. The new building was attached to an existing 1 million-square-foot hospital campus with connections on three levels. Connecting to an existing building presents the design team with a series of challenges when the existing building floor-to-floor heights are lower than desired for modern construction (a typical scenario). The design team coordinated with the owner over many meetings to work out the floor connections and transitions with an emphasis on patient flow to and from other departments.
The building heating, ventilation and air conditioning system consisted of central air handling units with hot water variable air volume reheat for local zone control. Each floor received a dedicated AHU, sized between 20,000 and 40,000 cubic feet per minute that had multiple direct-drive plenum supply fans. System redundancy was provided by dedicating a variable frequency drive for each supply fan and an electrical panel was dedicated to each AHU (see Figure 3).
Further redundancy was provided with a redundant AHU that was ducted into each of the clinical floor AHUs to allow any AHU to be taken out of service. The control system fully automates the process of tying the redundant AHU into any of the other four AHUs through a series of dampers. The logic sequence associated with the redundant AHU is as follows:
- A floor can only have one AHU assigned at a time.
- Each floor shall always have an AHU assigned.
- When the redundant AHU is assigned to a floor, the building automation system signals the fire alarm system to change the smoke damper association.
- Supply duct static sensors assigned to the floor served by the redundant AHU are reassigned and used to control supply fans.
- The building automation system uses the same cubic feet per minute offsets assigned to the AHU that was normally assigned to the floor being served by the redundant AHU.
With this arrangement, maintenance can be performed, including filter changes or cleaning, at any time of the day without interruption to patient care areas; and the AHU can be shut down properly during this time. The risk assessment for mechanical systems yielded a need for system redundancy (see Figure 4). Equipment was sized for an N+1 configuration and the quantity was determined by the expected minimum load.
Heating water was generated using three 3 million Btu per hour condensing-type boilers operating at 140 F for optimal efficiency. For cooling, three 250-ton air-cooled chillers were each paired with a pair of air-cooled condensing units. Similar redundancy was provided for four domestic hot water heaters serving the facility’s pumped hot water loops. Medical gas and medical vacuum systems also were dedicated for the facility with N+1 redundancy and expansion capability on multiplex skids.
To maximize the usable clinical space on four floors, the mechanical and electrical equipment was relegated to the basement and penthouse with rated chases through the building delivering utilities to each floor. Electrical and information technology rooms were stacked and centralized on each clinical floor to minimize cost and system complexity.
Electrical and technology systems
The electrical system distributed 480 volts to each electrical closet with step-down transformers at each floor and zone to improve reliability. The use of distributed step-down transformers in lieu of 208 volts distribution is intended to improve system reliability while reducing wiring costs. The primary voltage serving the new patient tower was 13.2 kilovolts, which came courtesy of new incoming service switchgear with two utility sources. The incoming service gear includes automatic throw-over controls to switch the campus to either source.
As a courtesy to the utility company, the switchgear has a split-bus main-tie-main arrangement so only half of the campus is moved at any time, limiting the switched load to less than 3 megawatts. The new patient tower features a double-ended unit substation with physically separated section and an interlocked tie breaker (see Figure 5). The north tower is fed with two separate 13.2-kilovolt feeders originating on either of the incoming switchgear split bus. This arrangement allows the new tower to be place on either utility feed, to improve system balancing and load management.
Not to be outdone by the normal distribution redundancy, the emergency power supply and emergency power supply system was dedicated to this addition with the ability to expand for the entire campus. New 4,160-volt paralleling gear was located at the central plant and paired with two relocated 4,160-volt generators. The paralleling gear and the associated EPS room were sized for three generators and a total of 3 megawatts of capacity.
Using 4,160-volt generators alleviated the cost of electrical feeders; the central plant was more than 1,000 feet away from the new patient tower. The tower has a dedicated EPSS unit substation with the space to add a second transformer and medium-voltage switch for a main-tie-main configuration, allowing for future expansion of system redundancy. The EPSS includes bypass-isolation, closed-transition transfer switches with three load stages.
- Stage 1: Life safety and critical branches.
- Stage 2: Automatic equipment branches.
- Stage 3: Delayed automatic equipment branches.
The use of closed-transition switches allows the facility to test generators using building load without disrupting hospital functions. This is important for getting accurate loads during times of peak usage while preventing computers and sensitive equipment from seeing a “blip” during transfer. All of the EPSS gear was located in a dedicated two-hour fire-rated room, separate from the normal equipment room. Doors into both rooms were sized for the unit substation transformers and a pathway for transformer removal/installation was coordinated with ceiling heights and building systems to allow for equipment replacement without disruption to other systems.
With a modern patient care facility, myriad low-voltage systems are present. The systems in this project included:
- Access control.
- Building automation system controls.
- Community antenna TV.
- Distributed antenna.
- Fire alarm.
- Information systems: copper.
- Information systems: fiber optic.
- Lighting controls.
- Nurse call.
- Patient telemetry.
- Voice over internet protocol.
- Wireless network access.
Managing the low-voltage system cables, providers and contractors requires frequent coordination during construction. One of the primary challenges is assigning responsibility for fire stopping. Premanufactured low-voltage fire-rated cable paths were provided at every rated wall and into every patient room to alleviate this coordination concern and allow for easy cable additions in the future.These systems also allow for cables to be added or removed without the need for the installer to replace putty in conduit pathways (see Figure 6).
During the planning of the new tower, it was determined that the phone, cable and internet service providers — along with fiber to remote buildings — conflicted with the new tower location. One of the make-ready projects performed was to revise the service access road and low-voltage provider routes. Temporary service routes were planned to make the site available during construction.
The new tower included a new service entrance room, sized 20-by-20-feet, which could eventually replace the existing service demark room, which is becoming increasingly buried in the facility. A fully supervised paging system was provided along with a new head-end message server to facilitate a future project to migrate the entire campus to a supervised system. The information systems rooms, like the electrical rooms, are sized for future campus expansion and system redundancy.
When designers are looking at the risk categories and assessment results for modern health care facilities, system redundancy becomes a topic that is less likely to make value engineering lists, which is a good thing for patients and the facility.